1. Field of Invention
The present invention relates to a method of manufacturing semiconductor devices. More particularly, the present invention relates to a method of reconditioning a reaction chamber and controlling the critical dimension of an etching layer.
2. Description of Related Art
After using a chemical vapor deposition (CVD) reactor or an etching reactor for a period of time, reacted material or high molecular weight material is often deposited on the interior surface of the reaction chamber. The coated material is only loosely attached to the reactor sidewalls. Hence, the material may easily come off to become polluting particles inside the reaction chamber during a subsequent process.
To prevent accumulation of too much pollution inside a reaction chamber, a CVD reactor or an etching reactor is dry-cleaned after a set period so that micro-particles attached to the interior sidewalls of the reaction chamber are removed. Furthermore, after a long period of operation and a definite number of dry cleanings, a preventive maintenance (PM) of the reaction chamber is often conducted to restore the reaction chamber to ideal operating conditions.
In a typical processing situation such as an etching operation, a few micro-particles often remain attached to the interior sidewalls of the reaction chamber. However, after dry cleaning or preventive maintenance, micro-particles are no longer attached to the interior surfaces of the reaction chamber. The micro-particle-free condition immediately after a dry cleaning or a preventive maintenance frequently leads to a lowering of the etching rate and a deterioration of etching uniformity. Hence, a seasoning step is required to recondition the reaction chamber after a dry cleaning or a preventive maintenance.
Conventionally, to recondition a reaction chamber after a dry cleaning or routine preventive maintenance, a dummy wafer is placed inside the reaction chamber. Thereafter, gases including trifluoromethane, carbon tetrachloride, argon and oxygen are introduced into the reaction chamber. Finally, an oxygen plasma etching is carried out for a prescribed period so that some micro-particles are again attached to the interior surfaces of the reaction chamber.
However, the aforementioned reconditioning method has several drawbacks, including:
1. To recondition the interior of the reaction chamber, an etching operation with oxygen plasma must be performed for over an hour after each dry cleaning or preventive maintenance. This is a long time.
2. Because more than an hour of oxygen plasma etching is required after each dry cleaning or preventive maintenance, the dummy wafer is consumed quickly. Hence, the dummy wafer placed inside the reaction chamber needs constant replacement. In addition, special gases need to be introduced into the reaction chamber during reconditioning, therefore increasing dry-cleaning and preventive maintenance cost.
3. Since the reconditioning after each dry cleaning and preventive maintenance is time consuming, the dry cleaning cycle is likely extended. However, by extending the dry cleaning cycle, more high-molecular-weight particles accumulate on the interior surfaces of the reaction chamber, leading to a shorter preventive maintenance cycle and reducing the utilization rate of the equipment.
4. After the reaction chamber is resumed, the gaseous nitrogen and oxygen are introduced into the reaction chamber to react with the etched layer, but the gaseous source can not easily control the critical dimension of the etched layer.
Accordingly, one object of the present invention is to provide a method of reconditioning a reaction chamber such that the reaction chamber can resume normal operation within the shortest possible period.
A second object of this invention is to provide a method of reconditioning a reaction chamber such that cost of dry-cleaning and preventive maintenance is reduced.
A third object of this invention is to provide a method of reconditioning a reaction chamber such that the preventive maintenance cycle for the reaction chamber is extended and the utilization rate of the equipment use time is increased.
A fourth object of this invention is to provide a method of controlling an etching layer such that the etched layer has vertical sidewalls and an accurate critical dimension.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of reconditioning the reaction chamber of an etching reactor. After several wafer etching operations, a dry cleaning or a preventive maintenance of the reaction chamber is carried out. After the dry-cleaning or preventive maintenance, gaseous nitrogen and hydrogen are introduced into the reaction chamber and a dummy wafer is placed inside the reaction chamber. A radio frequency (RF) power source is switched on to initiate a wafer etching operation. Photoresist material on the dummy wafer reacts with the gases inside the reaction chamber to form high molecular weight particles so that the reaction chamber is reconditioned within a very short time. Alternatively, instead of a dummy wafer, a production wafer that requires actual etching may be placed inside the reaction chamber after dry cleaning or preventive maintenance. To recondition the reaction chamber, gaseous nitrogen and hydrogen are introduced into the reaction chamber and then RF power is switched on to initiate wafer etching. The gases inside the reaction chamber react with the production wafer for rapid production of high molecular weight particles. Therefore, the reaction chamber is reconditioned in-situ in the wafer etching operation. In addition, the presence of gaseous nitrogen and hydrogen inside the reaction chamber makes the etching reaction of the production wafer proceed in a controlled manner. Hence, critical dimensions of the etched layer on the production wafer are more accurately controlled while nearly vertical sidewalls are produced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.